The present invention relates generally to a waveguide polarizer, and more specifically to waveguide polarizer differential phase error adjustment device.
Satellite antenna systems frequently utilize circularly polarized beams to send and receive communication signals. As one skilled in the art will appreciate, the circularly polarized beams can be generated in a number different of ways. For example, in many instances, a microwave polarizer can be used to convert linear polarized signals to circularly polarized signals. The polarizer essentially converts linearly polarized TE10 mode input signals into circularly polarized signals by decomposing the input linearly polarized signal (TE10 mode) into TE10 mode and TE01 mode signals and introducing a precise 90 degree phase shift between the two (TE10/TE01) modes. When the TE10 mode and TE01 mode signals propagate with equal amplitude and 90 phase difference, the signal is circularly polarized.
FIGS. 1a and 1b illustrate a well known corrugated square waveguide polarizer 100 used to create circularly polarized waves. This particular polarizer design simultaneously achieves a low input match of the TE10 and TE01 modes, as well as a precise 90-degree phase shift between the two orthogonal electric field modes over the usable frequency bands.
During design of the corrugated square waveguide polarizer 100, the 90-degree phase shift is accurately predicted using mode matching techniques and predictions confirmed by known measurements. Performance problems for the waveguide polarizer, however, can occur because of tolerances in the physical structure of the polarizer created during the manufacturing process. As one skilled in the art will appreciate, the phase shift is very sensitive to the fabricated dimensions of the polarizer.
In order to obtain less then 1 degree phase error, the polarizer needs to be fabricated with dimensional accuracy of <0.001″ at Ku/Ka bands. These very tight manufacturing tolerances are extremely difficult to achieve on a consistent basis and performance essentially comes down to how well you can manufacture the polarizer. Even the best manufacturing processes typically will create polarizers with tolerance errors that make the polarizers inoperable at certain frequencies. Thus, a device and/or method is needed that will offset or fix the phase shift errors caused by manufacturing tolerance errors.